1. Field of the Invention
The present invention relates to an improved process for the preparation of hydrogen peroxide by catalytic reaction between oxygen and hydrogen in a reaction medium in the presence of a catalyst. More particularly, the present invention relates to an improved process for the preparation of hydrogen peroxide by catalytic reaction between oxygen and hydrogen in a reaction medium containing substantially no halogen ion in the presence of platinum group metal catalyst.
2. Description of the Prior Arts
Processes mainly used for preparing hydrogen peroxide on an industrial scale are autooxidation processes using an alkylanthraquinone as a reaction medium. These processes have problems that reduction, oxidation, extraction and separation with water, purification, concentration and the like processes are complicated and costs for apparatuses and operation are high. Further, additional problems are encountered such as loss of alkylanthraquinones by deterioration and deterioration of activity of the hydrogenation catalyst.
In order to solve these problems, other process for the preparation of hydrogen peroxide have been proposed. One of such proposals is a process in which hydrogen peroxide is prepared directly from oxygen and hydrogen using a catalyst in a reaction medium. For example, a process has been proposed in which a platinum group metal is used as the catalyst for the preparation of hydrogen peroxide from oxygen and hydrogen. This process is known to be successful in preparing hydrogen peroxide in a considerably high concentration (cf., for example, U.S. Pat. Nos. 4,009,252, 4,279,883 and 4,772,458, and European Patent Application Laid-Open No. 0132294A1).
The conventional processes perform the reaction in a reaction medium having dissolved therein an acid or an inorganic salt. In particular, the selectivity of hydrogen peroxide and its concentration are increased by the addition of halogen ions in the reaction medium. For example, U.S. Pat. No. 4,772,458 supra describes that in the preparation of hydrogen peroxide from oxygen and hydrogen in an aqueous solution made acidic with sulfuric acid under pressure, copresence of halogen ions such as bromide ions in the aqueous solution makes it possible to prepare hydrogen peroxide selectively in a high concentration.
In preparing hydrogen peroxide by catalytic reaction between oxygen and hydrogen in a reaction medium, in order to obtain hydrogen peroxide in a practically acceptable high concentration by the aforementioned conventional processes, it has been considered indispensable to have an acid and halogen ions contained in the reaction medium. Thus, when halogen ions are present in a high concentration in an acidic reaction medium, the apparatus for handling the reaction mixture suffers severe corrosion and hence not only materials which can be used for such apparatuses are limited considerably but also the elution of the catalyst component into the reaction medium is unavoidable. In particular, the amount of the catalyst component eluted into the reaction medium increases proportionally to the concentration of halogen ions.
Such an elution of the catalyst component causes decrease in the activity of the catalyst and reduction in the lifetime of the catalyst. In addition, the metal, which is the catalyst component, eluted into the reaction medium not only deteriorates the quality or grade of hydrogen peroxide as the product but also it is difficult industrially to recover the catalyst component metal which eluted in a low concentration.
On the other hand, it is also known that the presence of halogen ions decreases the activity of the platinum group metal catalyst. Further, the above-described process requires expensive, anticorrosive materials for the reaction vessel and post treatment for the removal of halogen ions, if necessary for the purpose for which the resulting hydrogen peroxide is used, which incurs high cost.